1. Field of the Invention
The present invention relates to a hole transporting polymer, a method of producing the same, and an organic electroluminescence device (hereinafter referred to as an “organic EL device”, sometimes) using the hole transporting polymer.
2. Description of the Related Art
An inorganic electroluminescence device (hereinafter referred to as an “inorganic EL device”, sometimes) using an inorganic fluorescent substance has hitherto been used for a flat light source as backlight, a display device such as flat panel display or the like, but a high-voltage alternating current was required for driving the devices.
Tang et al. have recently fabricated an organic EL device having a two-layer structure, comprising a laminate of a light emitting layer of an organic fluorescent dyes and a layer of an organic charge transporting compound generally used in a photosensitive layer for electrophotography (U.S. Pat. No. 4,539,507). Since the organic EL device has a feature that emission of various colors can be easily obtained, in addition to low-voltage driving and high luminance, in comparison with the inorganic EL device, various attempts have been made and reported regarding the development and improvement of the device structure, organic fluorescent dyes and organic charge transporting compounds,etc [Jpn. J. Appl. Phys. Vol. 27, page L269 (1988); and J. Appl. Phys., Vol. 65, page 3610 (1989)]
As the hole transporting material, for example, various compounds such as oxadiazole derivatives, oxazol derivatives, hydrazone derivatives, triarylpyrazoline derivatives, arylamine derivatives, stilbene derivatives and the like have been reported.
In case of using only a low molecular weight hole transporting material in the organic EL device, the mechanical strength and heat resistance of the hole transporting layer were insufficient. As the method of forming a hole transporting layer, deposition under vacuum is generally used but has a problem of high production cost. To the contrary, there have been reported a lot of examples using the hole transporting polymer, such as organic EL device using a polystyrene derivatives having an aromatic amine group on the side chain (JP-A-8-259935), organic EL device using a polyester having an aromatic amine group(JP-A-8-259880) and the like, for the purpose of improving the durability and film-forming property. However, these organic EL devices are not necessarily satisfactory in view of the stability on driving.
On the other hand, in a photosensitive layer for electrophotography using the hole transporting material, like the organic EL device, the addition of a polysiloxane is performed for the purpose of preventing deterioration caused by corona discharge. Furthermore, there has been reported a hole transporting polysiloxane obtained by mixing a silicon hole transporting material with a curable polysiloxane and curing the mixture for the purpose of imparting the hole transporting property to the polysiloxane (JP-A-9-124943).
As an example of using a hole transporting polysiloxane in an organic EL, an organic EL device obtained by mixing a polysiloxane having a carbazole group on the side chain with a light emitting polymer has been proposed (WO 9501871).